This circuit conditions different signals of frequency below 1 kHz and displays their waveforms on the PC’s screen. The hardware is used to condition the input waveform and convert it to the digital format for interfacing to the PC. The
software for acquiring the data into the PC and displaying the same on its screen is written in Turbo C.
The input waveform (limited to 5V peak-to-peak) is first applied to a full-wave rectifier comprising op-amps A1 and A2 of quad op-amp LM324 (IC4) and a zerocrossing detector built around LM3914 dot/ bar display driver (IC8) simultaneously.The full-wave rectifier rectifies the in- SANI THEO put signal such that the negative half cycle
of the input signal is available in the positive side itself, so both the half cycles are read as positive when it is given as input to the ADC. During positive half cycle, diode D3 is on and diode D4 is off, and op-amps A1 and A2 act as inverters. Thus the output is a replica of the input. During the negative half cycle, diode D3 is off and diode D4 is on. With R2=R3=R4=R5=R6=R=330 ohms, the voltage (V) at inverting pin 2 of op-amp A1 is related to the input voltage (Vi) as follows:
Vi/R +V/(2R)+V/R=0
V= -(2/3)Vi
PC-BASED OSCILLOSCOPE
The final output voltage (Vo) at pin 7
of op-amp A2 is given by the following
relationship:
Vo=(1+R/2R)(-2Vi/3)= -Vi
As Vi is negative, the output voltage is positive. The zero-crossing detector detects whether the cycle is positive or negative. It is the most critical part of the circuit and if it operates improperly, the symmetry of the analogue signal displayed in the PC monitor gets affected. At the zero-crossing instant when the input signal transits to negative side, the zero-crossing detector informs the PC by taking pin 15 of 25- pin ‘D’ connector of the parallel port high.
software for acquiring the data into the PC and displaying the same on its screen is written in Turbo C.
The input waveform (limited to 5V peak-to-peak) is first applied to a full-wave rectifier comprising op-amps A1 and A2 of quad op-amp LM324 (IC4) and a zerocrossing detector built around LM3914 dot/ bar display driver (IC8) simultaneously.The full-wave rectifier rectifies the in- SANI THEO put signal such that the negative half cycle
of the input signal is available in the positive side itself, so both the half cycles are read as positive when it is given as input to the ADC. During positive half cycle, diode D3 is on and diode D4 is off, and op-amps A1 and A2 act as inverters. Thus the output is a replica of the input. During the negative half cycle, diode D3 is off and diode D4 is on. With R2=R3=R4=R5=R6=R=330 ohms, the voltage (V) at inverting pin 2 of op-amp A1 is related to the input voltage (Vi) as follows:
Vi/R +V/(2R)+V/R=0
V= -(2/3)Vi
PC-BASED OSCILLOSCOPE
The final output voltage (Vo) at pin 7
of op-amp A2 is given by the following
relationship:
Vo=(1+R/2R)(-2Vi/3)= -Vi
As Vi is negative, the output voltage is positive. The zero-crossing detector detects whether the cycle is positive or negative. It is the most critical part of the circuit and if it operates improperly, the symmetry of the analogue signal displayed in the PC monitor gets affected. At the zero-crossing instant when the input signal transits to negative side, the zero-crossing detector informs the PC by taking pin 15 of 25- pin ‘D’ connector of the parallel port high.
